Kai,

I installed the same TruTrak servos in my IV-P. To be sure they could not go over center, I installed “stop bolts” in the face of the TruTrak servo to limit the travel of the control arm. My servos already had #6 threaded holes on the face under the servo arm that I used for this. It takes some fiddling with the alignment and positioning to get it all to work properly, but probably worth the effort.  I considered drilling the holes out to #8 or #10, but after testing the mod when installed in the control system, I convinced myself that the #6 bolts were adequate, as the only time the controls would move far enough to touch the screw stops is if something comes loose or there is a malfunction of the normal stops.

Bob